I just managed to post a link to an uploaded schematic --- I think. Is it infact accessible/ legible? My intent was to ask for confirmation that I understand the recommended mods. Obviously, I'm a newbie and am staggering around the facilities.

I'm going to try sending a second drawing describing the output buffer.

I guess I missed the earlier posts by Sync from months back about the mad 339A mod pirate. Yes, That was my 339A that sold for $425 on Ebay.
Just an FYI,
I sold my 334A a couple of years back, it was in mediocre cosmetic condition, but it passed (and exceeded) all of its tests with flying colors and worked great. It was also completely original. I had the same type of auction with test details and pictures. It sold for about $215 + shipping, which if you watch those auctions you’ll know is about the top dollar for that piece of gear. Most sell for $100 - 150.

In the end, I’m no Tim Rawson or Chinese conglomerate. I’m not out to profit or build a company off the backs of others IP. I do try and contribute what I can to this forum and I expect that at times the things I create from my time here may be sold and occasionally that may increase the value of the item. I would think we’d all be happy about that because if mine is worth more money then yours probably is too, if you sell it properly…..

No problem. I bought several in various conditions but when they were dirt cheap. Now with some demand - too much IMO. But 100-150 for stock one is a good price range. I would like to know where you sourced replacement knobs. Most of them at their age are broken.

THx-Richard

BTW, Davada :-) CR14 hanging on the osc output -- a X1 buffer before it might reduce thd further ??? Have you tried that? may or may not make a difference (5.1Meg in series). but at -100dbv, everything matters.

[I cannot try it because I am in Bangkok for another month and don't have a 339 to play with.]

BSST, that is one way to attach images to the your post. Another way, after you press the QUOTE button to reply to a post and after you typed all the stuff you want, before pressing the SUBMIT REPLY button,

post. I'll try it and post it below. The image is handy and create a small preview as shown below.

Quote:

Originally Posted by RNMarsh

BTW, Davada :-) CR14 hanging on the osc output -- a X1 buffer before it might reduce thd further ??? Have you tried that? may or may not make a difference (5.1Meg in series). but at -100dbv, everything matters.

THx-Richard

Now that is interesting.

If I recall correctly, in something HP wrote, CR14 perhaps was causing (or a zener pair) was causing distortion and HP recommended using a higher value part. Prior to CR14, HPhad a circuit of other stuff in there and they changed it to the Resistor series w/Diode combo.

Then, are you suggesting an X1 buffer before the CR14 and the U3 change to LME4970? Now, maybe it was the CR11, CR13 zeners that were to change from 12.1 to 15.3v. I'll have to find the correct reference to it.

Finally, I always wondered about that dual 5Meg Switched Pot. If I could find one, I'd install it and see if it make a difference! I think we'd find some slightly better numbers with it as opposed to the old AB carbon comp pot. Like Davada found when he changed the 10K pot.

This is a stacked dual 5 Meg pot with a switch in it. I think it is the small 2 mm shaft like the bournes 10 K pot. Also, there is room enough for a standard sided pot body, instead of the mini square body this one is made from.

Richard while your over there, can you find a supplier that will provide 5 samples for testing of multiple HP339A untis to see if they will reduce distortion further?

Finally, I always wondered about that dual 5Meg Switched Pot. If I could find one, I'd install it and see if it make a difference! I think we'd find some slightly better numbers with it as opposed to the old AB carbon comp pot. Like Davada found when he changed the 10K pot.

This is a stacked dual 5 Meg pot with a switch in it. I think it is the small 2 mm shaft like the bournes 10 K pot. Also, there is room enough for a standard sided pot body, instead of the mini square body this one is made from.

Richard while your over there, can you find a supplier that will provide 5 samples of the dual 5Meg switched pot for testing of multiple HP339A untis to see if they will reduce distortion further?

If not Richard maybe Davada, or someone else can find samples that we could test and see if it works?

No problem. I bought several in various conditions but when they were dirt cheap. Now with some demand - too much IMO. But 100-150 for stock one is a good price range. I would like to know where you sourced replacement knobs. Most of them at their age are broken.

THx-Richard

BTW, Davada :-) CR14 hanging on the osc output -- a X1 buffer before it might reduce thd further ??? Have you tried that? may or may not make a difference (5.1Meg in series). but at -100dbv, everything matters.

[I cannot try it because I am in Bangkok for another month and don't have a 339 to play with.]

No problem. I bought several in various conditions but when they were dirt cheap. Now with some demand - too much IMO. But 100-150 for stock one is a good price range. I would like to know where you sourced replacement knobs. Most of them at their age are broken.

THx-Richard

Hi Richard,

The 100 - 150 pricing I referenced was in regards to an example I gave of an older HP 334A I sold. I think you may have confused that with the 339A auction info.

The knobs can be sourced through Ebay as well, you have to be patient and constantly monitoring though. Sometimes they show up but are ungodly expensive like $25 - 30 for a single knob, so you just have to pass. Then there's times that they show up at a really cheap price and they're gone quickly, like < 24hrs. So it really takes a determined effort to find them. Another option, one of the knobs I replaced I bought a replacement wing style knob and transferred the original skirt which was still in decent condition.